1. Field of the Invention
The invention relates to semiconductor integrated circuits and in particular to an on-chip inductor in differential operation.
2. Description of the Related Art
Many digital and analog elements and circuits have been successfully applied to semiconductor integrated circuits. Such elements may include passive components, such as resistors, capacitors, or inductors. Typically, a semiconductor integrated circuit includes a silicon substrate. One or more dielectric layers are disposed on the substrate, and one or more metal layers are disposed in the dielectric layers. The metal layers may be employed to form on-chip elements, such as on-chip inductors, by current semiconductor technologies. For on-chip inductor design, wireless communication chip designs more frequently employ differential circuits to reduce common mode noise, with inductors applied therein symmetrically.
As integrated circuit (IC) designs have progressed, there has been an increased interest in integrating several different functions on a single chip while minimizing process complexity and any resulting impact on manufacturing yield. This integration of several different functions on a single chip is known as system on chip (SOC). Additionally, with the rapid development of communication systems, an SOC typically includes radio frequency (RF) circuits and digital or baseband circuits. Since the RF circuits in a SOC are smaller than the digital or baseband circuits, chip fabrication employs a digital or baseband circuit process. Accordingly, the traces of inductors in SOC are thinner compared to the inductors of general RF circuits, resulting in reduction of quality factor (Q value). However, the signals with phase difference of 180° may pass through the adjacent traces of the inductor in differential operation, resulting in increase of parasitic capacitance. Thus, Q value cannot be increased by narrowing the space between traces of the inductor.
Since it is a trend of integrated circuit (IC) design to integrate different functions into a single chip, there is a need to develop an on-chip inductor with increased Q value.